U.S. patent number 4,547,588 [Application Number 06/248,924] was granted by the patent office on 1985-10-15 for process for producing methacrylic acid.
This patent grant is currently assigned to The Halcon SD Group, Inc.. Invention is credited to Sargis Khoobiar.
United States Patent |
4,547,588 |
Khoobiar |
* October 15, 1985 |
Process for producing methacrylic acid
Abstract
A catalyst composition useful for the oxidation of unsaturated
aldehydes, particularly the oxidation of methacrolein to produce
methacrylic acid, comprises the combination of oxides of
molybdenum, copper, phosphorus, antimony, and cesium and/or calcium
and optionally may include one or more of the elements Ni, Zn, Ru,
Rh, Pd, Pt, As, K, Rb, Sr, Ba, Cr, V, Nb, W, Mn, Re, and rare earth
metals including La.
Inventors: |
Khoobiar; Sargis (Kinnelon,
NJ) |
Assignee: |
The Halcon SD Group, Inc. (New
York, NY)
|
[*] Notice: |
The portion of the term of this patent
subsequent to March 5, 2002 has been disclaimed. |
Family
ID: |
26765552 |
Appl.
No.: |
06/248,924 |
Filed: |
March 30, 1981 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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81406 |
Oct 3, 1979 |
4271040 |
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973354 |
Dec 26, 1978 |
4374757 |
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972745 |
Dec 26, 1978 |
4252682 |
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972743 |
Dec 26, 1978 |
4252681 |
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973495 |
Dec 26, 1978 |
4252683 |
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27632 |
Apr 6, 1979 |
4240930 |
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27633 |
Apr 6, 1979 |
4261858 |
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27634 |
Apr 6, 1979 |
4261859 |
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27635 |
Apr 6, 1979 |
4261860 |
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47860 |
Jun 12, 1979 |
4377501 |
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Current U.S.
Class: |
562/535; 502/209;
502/211; 562/534; 562/600 |
Current CPC
Class: |
B01J
23/885 (20130101); B01J 23/8872 (20130101); B01J
23/8993 (20130101); B01J 27/186 (20130101); C07C
51/252 (20130101); C07C 51/252 (20130101); C07C
57/04 (20130101); B01J 2523/00 (20130101); B01J
2523/00 (20130101); B01J 2523/15 (20130101); B01J
2523/17 (20130101); B01J 2523/51 (20130101); B01J
2523/53 (20130101); B01J 2523/68 (20130101); B01J
2523/00 (20130101); B01J 2523/15 (20130101); B01J
2523/17 (20130101); B01J 2523/51 (20130101); B01J
2523/53 (20130101); B01J 2523/68 (20130101); B01J
2523/74 (20130101); B01J 2523/00 (20130101); B01J
2523/17 (20130101); B01J 2523/23 (20130101); B01J
2523/51 (20130101); B01J 2523/53 (20130101); B01J
2523/68 (20130101); B01J 2523/00 (20130101); B01J
2523/17 (20130101); B01J 2523/23 (20130101); B01J
2523/51 (20130101); B01J 2523/53 (20130101); B01J
2523/68 (20130101); B01J 2523/74 (20130101); B01J
2523/00 (20130101); B01J 2523/17 (20130101); B01J
2523/23 (20130101); B01J 2523/51 (20130101); B01J
2523/53 (20130101); B01J 2523/68 (20130101); B01J
2523/69 (20130101); B01J 2523/00 (20130101); B01J
2523/15 (20130101); B01J 2523/17 (20130101); B01J
2523/51 (20130101); B01J 2523/53 (20130101); B01J
2523/68 (20130101); B01J 2523/824 (20130101); B01J
2523/00 (20130101); B01J 2523/14 (20130101); B01J
2523/15 (20130101); B01J 2523/17 (20130101); B01J
2523/51 (20130101); B01J 2523/53 (20130101); B01J
2523/68 (20130101); B01J 2523/00 (20130101); B01J
2523/15 (20130101); B01J 2523/17 (20130101); B01J
2523/23 (20130101); B01J 2523/51 (20130101); B01J
2523/53 (20130101); B01J 2523/67 (20130101); B01J
2523/68 (20130101); B01J 2523/00 (20130101); B01J
2523/13 (20130101); B01J 2523/15 (20130101); B01J
2523/17 (20130101); B01J 2523/51 (20130101); B01J
2523/53 (20130101); B01J 2523/55 (20130101); B01J
2523/68 (20130101); B01J 2523/00 (20130101); B01J
2523/15 (20130101); B01J 2523/17 (20130101); B01J
2523/24 (20130101); B01J 2523/51 (20130101); B01J
2523/53 (20130101); B01J 2523/56 (20130101); B01J
2523/68 (20130101); B01J 2523/00 (20130101); B01J
2523/15 (20130101); B01J 2523/17 (20130101); B01J
2523/25 (20130101); B01J 2523/51 (20130101); B01J
2523/53 (20130101); B01J 2523/68 (20130101); B01J
2523/72 (20130101); B01J 2523/00 (20130101); B01J
2523/15 (20130101); B01J 2523/17 (20130101); B01J
2523/3706 (20130101); B01J 2523/51 (20130101); B01J
2523/53 (20130101); B01J 2523/68 (20130101); B01J
2523/847 (20130101); B01J 2523/00 (20130101); B01J
2523/15 (20130101); B01J 2523/17 (20130101); B01J
2523/27 (20130101); B01J 2523/3712 (20130101); B01J
2523/51 (20130101); B01J 2523/53 (20130101); B01J
2523/68 (20130101); B01J 2523/00 (20130101); B01J
2523/15 (20130101); B01J 2523/17 (20130101); B01J
2523/51 (20130101); B01J 2523/53 (20130101); B01J
2523/68 (20130101); B01J 2523/821 (20130101); B01J
2523/00 (20130101); B01J 2523/15 (20130101); B01J
2523/17 (20130101); B01J 2523/51 (20130101); B01J
2523/53 (20130101); B01J 2523/68 (20130101); B01J
2523/822 (20130101); B01J 2523/00 (20130101); B01J
2523/15 (20130101); B01J 2523/17 (20130101); B01J
2523/51 (20130101); B01J 2523/53 (20130101); B01J
2523/68 (20130101); B01J 2523/828 (20130101); B01J
2523/00 (20130101); B01J 2523/15 (20130101); B01J
2523/17 (20130101); B01J 2523/51 (20130101); B01J
2523/53 (20130101); B01J 2523/68 (20130101); B01J
2523/69 (20130101) |
Current International
Class: |
B01J
23/885 (20060101); B01J 27/186 (20060101); B01J
23/89 (20060101); B01J 23/887 (20060101); B01J
23/76 (20060101); B01J 27/14 (20060101); C07C
51/25 (20060101); C07C 51/16 (20060101); C07C
051/25 (); C07C 057/055 () |
Field of
Search: |
;562/534,535
;252/435,437 ;502/211 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1430337 |
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Jun 1976 |
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GB |
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1498595 |
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Jan 1978 |
|
GB |
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Other References
Parthasarath et al., Chemical Abstracts, 74:124846c,
(1971)..
|
Primary Examiner: Garner; Vivian
Attorney, Agent or Firm: Long; William C. Stewart; Riggs T.
Wells; Harold N.
Parent Case Text
CROSS-REFERENCE TO OTHER APPLICATIONS
This is a division of application Ser. No. 81,406 filed Oct. 3,
1979, now U.S. Pat. No. 4,271,040, which is a continuation-in-part
of U.S. Ser. Nos. 973,354, 972,745, 972,743 and 973,495, all filed
Dec. 26, 1978, now respectively U.S. Pat. Nos. 4,374,757,
4,252,682, 4,252,681 and 4,252,683 Ser. Nos. 027,632, 027,633,
027,634, and 027,635, all filed Apr. 6, 1979, now respectively U.S.
Pat. Nos. 4,240,930, 4,261,858, 4,261,859 and 4,261,860 and U.S.
Ser. No. 047,860 filed June 12, 1979, now U.S. Pat. No. 4,377,501.
Claims
What is claimed is:
1. A process for the preparation of methacrylic acid which
comprises oxidizing methacrolein in the vapor-phase with molecular
oxygen in the presence of a catalyst composition consisting
essentially of the composition expressed by the formula:
where: a=0.05-3; b=1-2; c=0.01-3; d=0.1-3; e=0.005-0.5; and x=a
value determined by the valence and proportions of the other
elements of the formula.
2. A process of claim 1 wherein b=1.2-1.8.
3. A process of claim 2 wherein b=1.3-1.7.
Description
PRIOR ART
This invention relates to a process and catalyst for the
vapor-phase oxidation with molecular oxygen of methacrolein to
methacrylic acid.
It is well known that unsaturated acids, such as acrylic acid and
methacrylic acid, can be produced by the vapor-phase oxidation of
the corresponding unsaturated aldehydes by means of molecular
oxygen in the presence of a suitable oxidation catalyst. A variety
of catalyst compositions have been proposed for this purpose. Many
such compositions comprise the oxides of molybdenum and phosphorus
in association with the oxides of various other elements, both
metallic and non-metallic. Of interest is U.S. Pat. No. 3,395,178
which discloses a preferred molybdenum-phosphorus atomic ratio of
10:1 which is considered to be optimum for a catalyst consisting
only of those two elements and disposed on a silicon carbide
support. Also, British No. 1,498,595 indicates that phosphorus is
effective in molybdenum-vanadium-phosphorus-cerium catalysts and
that with a ratio of Mo:P greater than 12:3 the activity is
decreased. However, in the molybdenum-phosphorus-vanadium-alkali
metal catalyst of U.S. Pat. No. 4,075,244, the phosphorus content
was varied between 0.5 and 3 (relative to Mo.sub.12) and no
particular significance was noted.
British Pat. No. 1,430,337 and U.S. Pat. No. 4,000,088 propose the
use of a catalyst composition in which the oxides of molybdenum and
phosphorus are combined with the oxides of antimony, and copper and
optionally with chromium. The catalyst does not contain cesium or
calcium.
U.S. patents disclosing related catalysts which may contain cesium
and calcium include U.S. Pat. Nos. 4,051,179, 4,042,533, and
4,042,625. In U.S. Pat. No. 4,051,179 the basic constituents are
molybdenum, phosphorus, and arsenic. Copper and vanadium are
treated as alternatives and while an alkali metal must be included,
antimony and calcium are considered optional. In U.S. Pat. No.
4,042,533 molybdenum, tungsten and vanadium are required, while
copper, phosphorus, and the alkali and alkaline earth elements are
optional and antimony is lacking. In U.S. Pat. No. 4,042,625,
magnesium and the alkali metals are added to molybdenum-phosphorus
catalysts, while calcium is optional and copper and antimony are
lacking. Examples of the catalyst include phosphorus levels of 1,
2, and 3 relative to Mo.sub.12, but no particular significance was
noted.
In U.S. Pat. No. 4,045,478 the use of calcium in
molybdenum-phosphorus catalysts is taught. The catalyst lacks
copper and the alkali metals while antimony is considered to be
only an optional ingredient.
U.S. Pat. No. 3,976,688 teaches a molybdenum-phosphorus catalyst
containing an alkali metal and a group of optional elements which
include barium, but not calcium. Copper and antimony are
lacking.
The catalyst disclosed in U.S. Pat. No. 4,042,533 also contains
rhenium as an optional ingredient. Still another prior art patent
disclosing the use of rhenium as an optional ingredient is U.S.
Pat. No. 3,956,378. While this catalyst requires the presence of
molybdenum and antimony, it lacks the alkali and alkaline earth
metals and copper and phosphorus are only optional ingredients.
Many other elements have been used in catalysts for preparation of
methacrylic acid by oxidation of methacrolein. U.S. patents which
disclose the use of elements of interest with respect to the
present invention include U.S. Pat. Nos. 4,001,316; 4,072,708;
4,138,365; 3,557,199; and 3,985,680. In these patents, as well as
those previously mentioned, the catalysts differ from those to be
disclosed hereinafter. The prior art catalysts generally are found
to require elements not included in the catalysts of the present
invention or some of the essential elements of the present
catalysts are lacking in prior art catalysts.
It has been found that catalysts for oxidation of methacrolein to
methacrylic acid have the characteristic property of remaining
stable for a period of time and then, without warning, of beginning
a rapid decline in activity. Consequently, an increase in the
useful activity of such catalysts has been sought.
Despite the many disclosures of the prior art, an improved catalyst
in this type is not developed merely by randomly selecting a group
of the many elements which have been disclosed. Small changes in
composition may be very important in achieving improved catalyst
performance and particularly in optimizing the catalyst composition
to suit, not only a specific reaction, but the desired operating
conditions also. The point is well illustrated by the improved
catalyst formulations to be described hereinafter.
SUMMARY OF THE INVENTION
It has been discovered that when using the catalysts to be
described to produce methacrylic acid by vapor phase oxidation of
methacrolein, it is possible to achieve both high activity and high
selectivity for extended periods of time. Broadly, the catalyst
composition comprises oxides of molybdenum, copper, phosphorus,
antimony, and cesium and/or calcium and the composition may include
one or more elements of Ni, Zn, Ru, Rh, Pd, Pt, As, K, Rb, Sr, Ba,
Cr, V, Nb, W, Mn, Re, and rare earth metals including La.
The catalyst composition used in the process of the invention also
may be expressed by the following general formula:
wherein A is cesium and/or calcium and B is Ni, Zn, Ru, Rh, Pd Pt,
As, K, Rb, Ca, Sr, Ba, Cr, V, Nb, W, Mn, Re, and rare earth metals
including La, and where a-e and x indicate the atomic ratio of each
component and, when a is 0.05-3, b is 0.1-5, c is 0.01-3, d is
0.1-3, e is 0-3, preferably 0.01-3, and x has a value which is
determined by the valence and proportions of the other elements in
the catalyst. Preferably, b will be 0.5-3, more preferably 1-2, and
most preferably about 1.2-1.8.
Specific embodiments of catalysts according to the invention
include catalysts containing cesium or calcium, alone or with
rhenium, according to the following formulas: Mo.sub.12 Cu.sub.a
P.sub.b Sb.sub.c Cs.sub.d O.sub.x or Mo.sub.12 Cu.sub.a P.sub.b
Sb.sub.c Ca.sub.d O.sub.x ; where a-d and x have the range of
values given above with the exception that b=1-2, preferably
1.2-1.8, and most preferably b=1.3=1.7; and Mo.sub.12 Cu.sub.a
P.sub.b Sb.sub.c Cs.sub.d Re.sub.e O.sub.x or Mo.sub.12 Cu.sub.a
P.sub.b Sb.sub.c Ca.sub.d Re.sub.e O.sub.x where a-e and x have the
range of values given above with the exception that b=1-2,
preferably 1.2-1.8, and most preferably b=1.3-1.7 c=0.01-3 and
e=0.005-0.5. Still another catalyst of the invention is represented
by the formula Mo.sub.12 Cu.sub.a P.sub.b Sb.sub.e Ca.sub.d W.sub.e
O.sub.x, again where a-e and x have the values given above with the
exception that b=1-2, preferably b=1.2-1.8.
When such a catalyst as has been described is in contact with a
vapor-phase mixture of methacrolein, molecular oxygen, steam, and
nitrogen at typical temperatures in the range of
250.degree.-400.degree. C. and pressures in the range of 0-5
atmospheres, excellent activity and selectivity to the production
of methacrylic acid is obtained for extended periods of time.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Catalyst Composition and Preparation
The catalyst of the invention comprises oxides or oxygen-containing
compounds of molybdenum, copper, phosphorus, antimony, and cesium
and/or calcium and optionally may include members of a group of
elements to be named. The catalyst may be represented by the
general formula:
wherein A is cesium and/or calcium and B is Ni, Zn, Ru, Rh, Pd, Pt,
As, K, Rb, Sr, Ba, Cr, V, Nb, W, Mn, Re and rare earth metals
including La, and where a-e and x indicate the atomic ratio of each
component relative to Mo.sub.12 and, when a is 0.05-3, b is 0.1-5,
c is 0.01-3, d is 0.1-3, e is 0-3, preferably 0.01-3, x is a value
determined by the valence and proportions of the other elements in
the catalyst. Preferably, b will be 0.5-3, more preferably 1-2, and
most preferably about 1.2-1.8. Preferred catalysts include those in
which component B is tungsten or rhenium. Other elements, which may
be included in minor amounts in the catalyst formulation in order
to promote catalyst activity or selectivity and without losing the
advantages to be shown for the general formula, are considered to
be within the scope of the invention. The catalyst composition may
be regarded either as a mixture of oxides of the named elements or
as oxygen-containing compounds of the elements or both. As prepared
and/or under reaction conditions, the catalyst may contain either
or both forms and both are intended to be included within the
phrase "mixtures of oxides."
The catalyst composition is preferably used in unsupported form,
e.g. in the form of pellets or other like compressed shapes of
various sizes, although conventional supports could be employed
instead. The composition may be formed in conventional manner using
techniques well known to persons skilled in the art. For example,
compounds of molybdenum, copper, phosphorus, antimony, cesium, and
rhenium are dissolved in a small amount of water or other solvent,
and the solutions are then combined and evaporated to dryness, e.g.
in a rotary dryer. The several components can be introduced into
solution in the form of various salts or other compounds of
convenient types and no specific form for the catalyst precursors
is necessary. The use of ammonium salts, halides, e.g., chlorides,
nitrates or acid forms of the elements, e.g., phosphoric acid, are,
however, particularly suitable. Preferably, however, aqueous
solutions are employed and water-soluble forms of the elements are
used. In some cases the solutions may have acids and/or bases added
to them to facilitate dissolution of the catalyst precursors. For
example, acids such as hydrochloric or nitric acid, or bases such
as ammonium hydroxide, can be used as desired. The resulting powder
from the evaporation is then thoroughly dried and preferably
screened to eliminate large particles which make it difficult to
produce uniform compressed shapes, such as pellets. Typically, the
powder is passed through a 20-mesh screen. The powder is then mixed
with an organic binder which can be of any conventional type, such
as polyvinyl alcohol, and the mixture is thoroughly dried and again
screened, typically to provide a 20-60 mesh size. The dried mixture
is then preferably combined with a lubricant, again of any
conventional type, such as stearic acid or graphite, and compressed
into the desired shape, e.g. pelletized, the compressed shapes
typically having heights and diameters of 1/16 inch to 3/8 inch.
Finally, the thus produced catalyst composition is activated at
high temperature for a prolonged period in accordance with
conventional practice in this art. For example, the pellets are
placed in an oven or kiln, or in a tube through which air is
passed, at an elevated temperature (e.g. 300.degree.-500.degree.
C., preferably 325.degree.-450.degree. C.) for at least ten hours.
In a particularly preferred activation step, the temperature is
raised at the rate of 20.degree. C. per hour to a maximum of
420.degree. C., preferably 320.degree.-400.degree. C., and this
temperature is maintained for 8 hours.
It will be understood that the foregoing description regarding
preparation of the catalyst in a form suitable for use in a
vapor-phase oxidation reaction is merely illustrative of many
possible preparative methods, although it is a particularly
suitable method and is preferred.
Methods of Operation
The catalysts described are generally useful for the production of
unsaturated acids by oxidation with molecular oxygen of unsaturated
aldehydes, although the reaction of methacrolein to form
methacrylic acid is of particular interest. Other possible starting
materials are the monoethylenically unsaturated aliphatic
monoaldehydes of from 3 to 6 carbon atoms, such as acrolein,
crotonaldehyde, 2-methyl-2-butenal, and the like, or mixtures
thereof.
The reaction in which the catalyst compositions of this invention
are of particular utility and in which they provide high
conversions and selectivities involves contacting the catalyst with
methacrolein and oxygen in the vapor phase, preferably also in the
presence of steam and diluents. When the catalyst of this invention
is used in the vapor-phase oxidation of methacrolein to form
methacrylic acid, the oxidation conditions employed are those
generally associated with this reaction, although it is preferred
that the molar ratio of oxygen to methacrolein should be kept at a
high value near the flammable range. Once reaction is begun, it is
self-sustaining because of its exothermic nature. A variety of
reactor types may be employed such as fluid or fixed bed types, but
reactors having the catalyst disposed inside a multiplicity of heat
exchanger tubes are particularly useful and convenient.
The gaseous feed to the reactor contains appropriate concentrations
of methacrolein, oxygen and steam and usually an inert gas is also
present, such as nitrogen and the like. The oxygen is usually added
as such or as air, which may be enriched with oxygen. As mentioned,
conventional oxidation conditions can be employed, but it is a
feature of the catalyst of this invention that methacrolein can be
present in concentrations of more than 5 up to about 20 volume
percent of the total feed with a preferred range of more than 5 up
to about 15 volume percent. In general at least 6 volume percent of
the aldehyde is used in the feed. The corresponding ranges for
oxygen are 3 to 15 volume percent, preferably 5 to 12 volume
percent and for steam up to 50 volume percent, preferably 5 to 35
volume percent, the balance being the inert gas or gases.
The temperature of the reaction should, for best results, be within
the range of from about 270.degree. to 450.degree. C., preferably
280.degree.-400.degree. C., and the optimum temperature range is
290.degree. to 325.degree. C. Because the reaction is exothermic,
means for conducting the heat away from the reactor are normally
employed to avoid a temperature increase which favors the
destruction of methacrolein by complete oxidation to carbon oxides
and water. The reactor temperature may be controlled by
conventional methods such as by surrounding the catalyst-containing
tubes with a molten salt bath.
The reaction may be conducted at atmospheric, superatmospheric or
subatmospheric pressure. Preferably, however, pressures are
employed ranging from atmospheric up to about 8 kg/cm.sup.2
absolute, preferably up to about 6.3 kg/cm.sup.2 absolute, and most
preferably up to about 4.5 kg/cm.sup.2 absolute.
The unsaturated acid product may be recovered by a number of
methods well known to those skilled in the art. For example, the
acid may be condensed, or scrubbed with water or other suitable
solvents, followed by separation of the unsaturated acid product
from the scrubbing liquid. The gases remaining after the
acid-removal step may be recycled to the reaction preferably after
removal of CO.sub.2 by conventional means, e.g., absorption in
aqueous carbonate solution.
The features of the invention will be more readily apparent from
the following specific examples of typical catalyst preparation and
its use in the oxidation of methacrolein. It will be understood,
however, that these examples are for the purpose of illustration
only and are not to be interpreted as limiting the invention.
EXAMPLE 1
Catalyst Preparation
In 750 cc of water are dissolved 636 grams of (NH.sub.4).sub.6
MO.sub.7 O.sub.24.4H.sub.2 O. Then 21.7 grams of
Cu(NO.sub.3).sub.2.3H.sub.2 O are dissolved in 100 cc of water,
58.4 grams of CsNO.sub.3 are dissolved in 150 cc of water, 20.5
grams of SbCl.sub.3 are dissolved in a mixture of 30 cc of water,
and 10 cc of concentrated HCl and 34.5 grams of H.sub.3 PO.sub.4
are dissolved in a mixture of 100 cc of water and 50 cc of 58%
NH.sub.4 OH solution. These solutions are mixed with 400 cc of 58%
NH.sub.4 OH and fed to a rotary dryer of 4000 cc capacity and the
mixture is evaporated to dryness at a temperature reaching a
maximum of 140.degree.-200.degree. C. The resulting powder is
removed from the dryer and dried in an oven at 200.degree. C. for 4
hours. The dried powder is screened through a 20-mesh screen, a 4%
aqueous solution of polyvinyl alcohol is added in sufficient
quantity to make a damp mixture and this mixture is dried at
75.degree.-80.degree. C. until the moisture content falls to 2-4
wt.%. The dried mixture is then screened to 20-60 mesh size
particles, and about 2-6% of stearic acid powder is thoroughly
mixed with it. The resulting mixture is then pelletized to form
pellets of 3/16 inch height and diameter in which the catalyst
components molybdenum, copper, phosphorus, antimony, cesium are
present (by calculation) in the atomic ratios of 12, 0.3, 1, 0.3
and 1, respectively. The pellets are then activated in any oven by
heating them to 100.degree. C. in one hour and then raising the
temperature gradually at a rate of about 20.degree. C. per hour to
370.degree. C. and maintaining them at this temperature for 8
hours. The catalyst is tested according to the procedure of Example
2.
EXAMPLE 2
Catalyst Testing
A 150 cc quantity of the catalyst composition of Example 1 is
placed in a reactor defined by a 1/2".times.90" stainless steel
pipe, the reactor pipe being filled with 50 cc of inert filler
(silicon carbide) below the catalyst bed and 100 cc of the inert
filled above the catalyst bed in conventional manner to insure
uniform temperature contact with the catalyst. Nitrogen-diluted
mixtures containing methacrolein, oxygen and steam are fed to the
reactor at a pressure of 1.74 kg/cm.sup.2 (absolute) and at a space
velocity of about 1200 hr.sup.-1. The term "space velocity" is used
in its conventional sense to mean liters of gas (at standard
temperature and pressure) per liter of catalyst per hour. The feed
composition is approximately, by volume, 6-7% methacrolein, 11-12%
oxygen and 20% steam, the balance being nitrogen, determination
being made on a wet basis. The reaction is run continuously and the
exit gas is analyzed at intervals of several hours. Analyses are
carried out by means of gas chromatography and by infrared
spectrography using conventional techniques. The average amount of
methacrylic acid produced is determined periodically and the
reactor temperature is adjusted as necessary to obtain the desired
yield, that is, the product of the conversion and the selectivity,
which for purposes of the comparisons to be made is about 0.15 gm
of methacrylic acid per hour per gram of catalyst.
EXAMPLE 3
A catalyst is prepared according to the method of Example 1 except
that the phosphorus content is increased to provide a catalyst
having the following nominal composition (by calculation):
The catalyst is tested according to the method of Example 2.
EXAMPLE 4
A catalyst is prepared according to the method of Example 1 but
having a higher phosphorus content than the catalyst of Example 3,
providing a catalyst having the following nominal composition (by
calculation):
The catalyst is tested according to the method of Example 2.
The results of the tests carried out on the catalysts of Examples
1, 3, and 4 are summarized in the following Table I.
TABLE I ______________________________________ Selectivity to
Activity Phosphorus Temp. Methacrylic Coeff. K Cat. Content(a)
Hours .degree.C. Acid(b) (c) ______________________________________
1 1 35 293 77 23 80 323 74.5 6 3 1.5 150 298 77.6 26 200 296 79.7
26 4 2 26 320 70 10 122 324 65 7
______________________________________ (a)relative to Mo.sub.12
(b)percent of methacrolein reacted which is converted to
methacrylic acid (c)a value calculated from experimental data to
provide a measure of catalyst activity and derived from the
equation: K = F.multidot. X.multidot. S.multidot. C.sup.E/RT where:
F = methacrolein concentration in feed S = space velocity of feed
gas X = conversion of methacrolein E = activation energy, 25,000
kcal/mol. R = gas constant T = absolute temperature
As explained in Example 2 the catalysts are operated to provide a
constant predetermined yield of methacrylic acid. In order to
provide a proper comparison, the performance of a catalyst is
reported at the period of time where the catalyst activity has
stabilized after an initial break-in period. This may mean, as in
Table I, that the time selected for comparisons is not the same if
the catalyst performance differs significantly. A stable period at
150-200 hours could be established readily for the catalyst of
Example 3, while the catalysts of Examples 1 and 4 had relatively
poorer performance and their activities declined earlier, as
indicated by the data. It is clear that the catalyst of Example 3
is superior to those of Examples 1 and 4, since it operated
consistently at a lower temperature and with higher activity and
selectivity after the other catalysts had lost significant
activity. Thus, is is concluded that catalysts containing
molybdenum, copper, antimony, and cesium are sensitive to the
phosphorus content. An optimum level should be found between a
phosphorus level of 1 and 2 (relative to Mo.sub.12). It is believed
that the optimum level is located between P.sub.1.2 and P.sub.1.8,
particularly between P.sub.1.3 and P.sub.1.7.
EXAMPLE 5
A catalyst corresponding to that of Example 1 is prepared by the
same general technique except that 5 grams of perrhenic acid
dissolved in 100 cc of water are included in the initial solution
to provide rhenium in a catalyst having the following nominal
composition (by calculation):
EXAMPLE 6
A catalyst is prepared according to the general method of Example 5
except that the amount of phosphorus is increased to produce a
catalyst having the following nominal composition (by
calculation).
The catalyst is tested according to the methods of Example 2.
EXAMPLE 7
A catalyst is prepared according to the method of Example 5 but the
amount of phosphorus is doubled to provide a catalyst having the
following nominal composition (by calculation):
The catalyst is tested according to the procedures of Example
2.
The results of testing the catalysts of Examples 5, 6, and 7 are
summarized in the following Table II, to which the footnotes of
Table I also apply.
TABLE II ______________________________________ Selectivity to
Activity Phosphorus Temp. Methacrylic Coeff. K Cat. Content(a)
Hours .degree.C. Acid(b) (c) ______________________________________
5 1 150 292 75 26 200 293 75.5 26 6 1.5 150 279 77 46.6 250 279 77
40 7 2 150 311 73.6 11.6 250 311 76 12
______________________________________
As in Table I, the catalysts are operated to provide the same yield
of methacrylic acid and the performance is reported during a stable
period of operation after the initial break-in of the catalyst. It
will be clear that the catalysts having rhenium added have better
performance than those of Table I, which contain no rhenium, since
they have higher activity and suggest improved aging
characteristics, especially with respect to the comparison of
catalysts 5 and 7 with catalysts 1 and 4. The rhenium-containing
catalysts also are sensitive to the phosphorus content and an
optimum value again appears between P.sub.1 and P.sub.2 (relative
to Mo.sub.12). It is believed that the optimum value is between
P.sub.1.2 and P.sub.1.8, particularly between P.sub.1.3 and
P.sub.1.7.
Taking the results of Tables I and II together, it may be concluded
that the ratio of molybdenum to phosphorus for catalysts of this
type will show an optimum performance at ratios between 12/1 to
12/2.
EXAMPLE 8
A catalyst is prepared according to the general method of Example 1
except that 79.2 gms of Ca(C.sub.2 H.sub.3 O.sub.2).sub.2.XH.sub.2
O are substituted for cesium nitrate and no aqueous ammonia is
added and a catalyst having the following nominal composition (by
calculation) is produced:
This catalyst is tested according to the methods of Example 2 and
the significance of the phosphorus to molybdenum ratio to catalyst
performance is shown. The catalyst is operated at about 304.degree.
C. for a period between about 20 to 80 hours with a selectivity of
76.3 and an activity coefficient of 18.6.
EXAMPLE 9
A catalyst is prepared according to Example 8 except that 5 grams
of Re.sub.2 O.sub.7 dissolved in 100 cc of water is included in the
solution to provide rhenium a catalyst having the following nominal
composition (by calculation):
The catalyst is tested according to the method of Example 2. The
significance of the phosphorus to molybdenum ratio to catalyst
performance is shown. The catalyst is operated at about 286.degree.
C. for a period between about 30 to 200 hours with a selectivity of
75.2 and an activity coefficient of 42.
EXAMPLE 10
A catalyst is prepared according to the general method of Example 9
except that instead of rhenium, tungsten is included and no aqueous
ammonia is used to provide a catalyst having the following nominal
composition (by calculation):
The catalyst is tested according to the method of Example 2 and the
significance of the phosphorus to molybdenum ratio to catalyst
performance is shown. For a period between about 20 to 170 hours
the catalyst is operated at about 302.degree. C., with a
selectivity of about 76.5 and an activity coefficient of about
22.4.
EXAMPLE 11
A catalyst is prepared according to the general method of Example 1
except that the phosphorus level is increased and palladium is
included to produce a catalyst having the following nominal
composition:
The catalyst is tested under the conditions of Example 2 and the
significance of the phosphorus to molybdenum ratio with respect to
catalyst performance is shown.
EXAMPLE 12
A catalyst is prepared according to the general method of Example 1
except that the phosphorus level is increased and rubidium is added
to produce a catalyst having the following nominal composition:
The catalyst is tested under the conditions of Example 2 and the
significance of the phosphorus to molybdenum ratio with respect to
catalyst performance is shown.
EXAMPLE 13
Other suitable catalysts in accordance with the invention are
prepared according to the general method of Example 1 and have the
following nominal compositions:
Mo.sub.12 Cu.sub.0.3 P.sub.2 Sb.sub.0.3 Cs.sub.0.3 Ca.sub.0.7
Cr.sub.0.3 O.sub.x
Mo.sub.12 Cu.sub.0.3 P.sub.2 Sb.sub.0.3 Cs.sub.0.3 K.sub.0.7
V.sub.0.3 O.sub.x
Mo.sub.12 Cu.sub.0.3 P.sub.2 Sb.sub.0.3 Cs.sub.0.3 Sr.sub.0.7
Nb.sub.0.3 O.sub.x
Mo.sub.12 Cu.sub.0.3 P.sub.1.7 Sb.sub.0.3 Cs.sub.0.3 Ba.sub.0.7
Mn.sub.0.3 O.sub.x
Mo.sub.12 Cu.sub.0.3 P.sub.1.2 Sb.sub.0.3 Cs.sub.1 La.sub.0.7
Ni.sub.0.3 O.sub.x
Mo.sub.12 Cu.sub.0.3 P.sub.1 Sb.sub.0.3 Cs.sub.0.3 Ce.sub.0.7
Zn.sub.0.3 O.sub.x
Mo.sub.12 Cu.sub.0.3 P.sub.1 Sb.sub.0.3 Cs.sub.1 Ru.sub.0.1
O.sub.x
Mo.sub.12 Cu.sub.0.3 P.sub.0.5 Sb.sub.0.3 Cs.sub.1 Rh.sub.0.03
O.sub.x
Mo.sub.12 Cu.sub.0.3 P.sub.1 Sb.sub.0.3 Cs.sub.0.3 Pt.sub.0.03
O.sub.x
Mo.sub.12 Ca.sub.0.3 P.sub.1.5 Sb.sub.0.3 Cs.sub.1 W.sub.0.5
The catalysts are tested under the conditions of Example 2 and the
significance of the phosphorus to molybdenum ratio with respect to
catalyst performance is shown.
* * * * *